High molecular weight stabilizer compounds for stabilizing polymers

ABSTRACT

A high molecular weight stabilizer compound formed as an ester of 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoic acid, or structural variants thereof, to impart improved resistance to the effects of ultraviolet radiation to polycarbonate comprising polymers, a process for the preparation of said compound, and articles of manufacture comprising said compound.

This is a divisional of application Ser. No. 08/631,592 filed on Apr.12, 1996, now U.S. Pat. No. 5,807,963 which is a divisional of Ser. No.08/361,264 filed on Dec. 21, 1994, which is now issued U.S. Pat. No.5,523,379.

FIELD OF THE INVENTION

The present invention relates to a composition having a high molecularweight useful either singly or in combination as a stabilizer forvarious polymeric materials. More particularly, the present inventionrelates to a polycarbonate, copolyestercarbonate, or polysiloxanecopolycarbonate wherein the chain terminating functional groups act toimpart a stabilizing function to the polymer molecule. Moreparticularly, the stabilizing function imparted to the polymer moleculeis an improved resistance to the deleterious effects of ultravioletradiation.

The present invention also provides a method of preparing thecomposition of the invention. Further the present invention alsoprovides for articles of manufacture comprising the composition of thepresent invention.

BACKGROUND OF THE INVENTION

Polycarbonates, copolyestercarbonates, and polysiloxane copolycarbonatesare high polymers produced by the condensation or intercondensation of adihydroxy compound and a diacid or reactive derivative thereof such asan acid halide. When the dihydroxy compound is bisphenol-A and the acidderivative is phosgene, a simple polycarbonate (PC) polymer results.Similarly terephthalic acid and ethylene glycol intercondense to formpolyethylene terephthalate (PET). Since these polymers are polyesters ofbifunctional precursor monomers, it is theoretically possible for thereaction mixture to go entirely to completion and create one entirereaction vessel filling molecule. In practice, of course, this does notoccur because as the polymerization increases the average chain lengthof the polymer increases, the viscosity of the reaction medium increasesand the reaction probability decreases because there are progressivelyfewer complementary reactive species in a unit volume of the reactionvessel. Thus the reaction slows and eventually terminates on the basisof the statistics of reaction probability and the statistics of thepolymer chain conformation because a reactive acid-derived terminus isstatistically unlikely to find and react with a reactive hydroxylterminus.

In producing these types of polyester polymers, endcapping or chainterminating agents are employed. In order to effectively terminate thegrowing end of a polymer molecule, these chain terminating or endcappingspecies must be monofunctional such that when reaction occurs with thegrowing end of the polymer molecule, further growth in the chain lengthof the particular polymer molecule is terminated. Thus depending on thestatistical mechanics of polymer growth, there should be at least arough correlation between the quantity of chain terminating agent, on amolar basis, and the average molecular weight of the polymer. Indeed,one function of endcapping agents, aside from the elimination ofreactive ends, is to regulate the average molecular weight of thepolymer being synthesized.

Typical endcapping agents have been monofunctional compounds of lowmolecular weight, high reactivity, readily available and cheap.Additionally such compounds have been monofunctional analogs of one orthe other bifunctional monomers being polymerized. Thus in the case ofpolycarbonates, typical endcapping agents are various phenols such asphenol, tertiary-butyl-phenol, and para-cumyl-phenol. Other endcappingagents have been disclosed such as chromanyl in U.S. Pat. No. 3,697,481to Bialous et al. herewith incorporated by reference. In general,aromatic polycarbonates and polycarbonate copolymers may be produced byvarious methods such as shown in U.S. Pat. Nos. 3,635,895 and 4,001,184,herewith incorporated by reference.

Variations in the mole ratio between the chain terminating compounds,such as phenol, and the chain growing compounds, such as bisphenol-A andphosgene, lead to the ability to control the molecular weight of theresulting polymer. Higher levels of chain terminating agents in thereaction mixture tend to lead to lower average molecular weights orshorter average polymer chain length. Conversely, lower levels of chainterminating agents in the reaction mixture tend to lead to higheraverage molecular weights or longer average chain length.

Frequently there are additional considerations or advantages associatedwith the choice of a particular chain terminating agent. Being esters,polymers such as polyesters, copolyestercarbonates, polycarbonates,polysiloxane copolycarbonates and the like are susceptible to hydrolysisand trans-esterification. A chain terminating agent that reduces thesusceptibility of these polymers to hydrolysis or trans-esterificationcan impart improved properties to the polymer as well as functioning asa polymer chain length regulator during synthesis.

When put to use, these polymers may be alloyed with other polymersand/or compounded with various stabilizing and functionalizingadditives. The additive compounds or mixtures of additive compounds aretypically incorporated to prohibit undesired reactions of the polymer tothe physical or chemical challenges experienced either during theprocess of converting the polymer to a useful article of manufacture orduring the useful life of the manufactured article containing thestabilized polymer. These physical and chemical challenges include amongothers, slow oxidation, rapid oxidation (combustion), photolyticdegradation, thermal degradation, and hydrolytic degradation.Consequently, depending on a particular polymer, there are to be foundvarious stabilizer compounds available commercially either singly or incombination that improve or render more stable one or more of thephysical or chemical properties of the polymer.

A particular problem associated with the polycarbonate family ofpolymers is stability to photolytic degradation, especially that causedby ultraviolet radiation. There are accordingly a large variety ofstabilizer compounds useful to impart an improved resistance to theeffects of ultraviolet radiation upon polycarbonate polymers. Amongthese stabilizer compounds are the phenolically substitutedbenzotriazole compounds. At low levels of addition to the polymerformulation, below about 0.5 to about 1.0 weight percent, thebenzotriazole ultraviolet stabilizers generally disperse or dissolve inthe polymer matrix in a satisfactory fashion and generally impart thedesired ultraviolet resistance to the polymer. At higher levels, aboveabout 2 to about 3 weight percent, the benzotriazole stabilizers have atendency to undergo migration, phase separation, and plate out. This isa significant problem for certain extruded, laminated or layered sheetformulations where the function of the sheet is to provide a protectivefunction for structural or glazing sheet thereunder, because when thestabilizer compound undergoes a phase separation the effective quantityof stabilizer compound present in the polymer matrix is reduced.Additionally, the stabilizer that migrates form the polymer matrix coatsand/or plugs the manufacturing process equipment, causing surfacedefects and other quality problems in the articles being manufactured.This results in increased downtime of the manufacturing equipment forcleaning.

A previous approach exemplified by the teachings of U.S. Pat. No.4,153,780 (the '780 patent) where phenolically substitutedbenzotriazoles, active for imparting ultraviolet resistance to polymers,are chemically bound as an endcapping agent to the polycarbonate polymerthrough the phenolic hydroxyl moiety. This approach incorporates thephenolically substituted benzotriazole as a chain stopping agent intothe polymeric molecule. However, by the formation of a covalent chemicalbond between the phenolic oxygen of the substituted benzotriazole andthe terminal chloroformate group of the growing polycarbonate polymer,the ability of the phenolically substituted benzotriazole to function asan ultraviolet stabilizer is greatly reduced or altogether destroyed.Apparently, the phenol hydroxyl group of the phenolically substitutedbenzotriazole must be capable of forming a hydrogen bond in order forthe molecule to function as an inhibitor for the degradative effects ofultraviolet radiation. While Applicant subscribes to this view as amatter of information and belief as however, the operability ofApplicant's invention does not depend on this particular theoreticalmechanism. While the incorporation of the benzotriazoles as taught inthe '780 patent may render polycarbonates somewhat more stable toultraviolet radiation, on a comparative basis the addition of anequivalent amount of free, as opposed to polymer bound, benzotriazolestabilizer compound to polycarbonates generally produces a betterstabilizing effect in the polymers being treated therewith.Consequently, the benefit that might be achievable by chemicalincorporation of the stabilizer molecule into the polymer is more thanoffset by a loss in efficacy caused by the changes in chemical bondingforced upon the stabilizer molecule when the stabilizer molecule isincorporated into the polymer.

Typically the stabilizer compounds are of a significantly lowermolecular weight by comparison to the polymer being stabilized. Thislarge difference in molecular weight leads to problems that aregenerally categorized as compatibility problems, i.e. the stabilizer maynot be soluble in the polymer or because of its low molecular weight,the stabilizer has a tendency to volatilize or migrate out of thepolymer matrix. A stabilizer that will not dissolve or disperse in thepolymer to be stabilized does not impart any useful benefit to thepolymer. Likewise a stabilizer that volatilizes or migrates out of thepolymer matrix also does not impart any useful benefits to the polymer,and causes problems during manufacturing. The famous so-called "new car"smell is due to the migration and/or volatilization of various polymerstabilizing additives and plasticizers from the polymeric formulationswidely employed in the manufacture of automobiles.

STATEMENT OF THE INVENTION

Thus it is desirable to have stabilizer compounds that function tostabilize polymers that are chemically bound to the polymer or polymeralloy being stabilized, thereby eliminating the problems that occur dueto lack of solubility, migration, or volatility. Applicant hasdiscovered a method of chemically incorporating into the polycarbonatepolymer or polycarbonate copolymer molecule, compounds effective forstabilizing polycarbonate against the degradative and deleteriouseffects of ultraviolet radiation, the stabilizing properties of whichare not affected by chemical incorporation into the polymers.

The present invention thus provides for a high molecular weight compounduseful for stabilizing polymers against the effects of ultravioletradiation generally comprising: (a) a condensation product comprisingboth (i) a bis-phenol derivative and (ii) a phosgene derivative or acarbonate ester, and (b)3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid or structural variant thereof as an end capping agent for saidcondensation product wherein said end capping agent is chemically boundto said condensation product by an ester linkage and wherein themolecular weight of said high molecular weight compound is at least1,125; the exception being the di-ester of a bis phenol compound with3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid will also act as a stabilizer and when the bis phenol is bis phenolA the molecular weight is 871. Such a di-ester compound may be generallydescribed as a compound of the formula: ##STR1## where each R⁵ isindependently selected from the group consisting of hydrogen, alkylgroups of from one to about nine carbon atoms, and aryl groups of fromsix to about fifteen carbon atoms, and E is an esterified acid selectedfrom the group of acids having the formula: ##STR2## where R₁ isselected from the group of two to twelve carbon atom alkyl groups,preferably branched alkyl groups containing four to twelve carbon atoms,R₂ is selected from the group of hydrogen or one to twelve carbon atomalkyl groups and n varies from 0 to 20; wherein the molecular weight isat least 871. The present invention further provides for such a highmolecular weight compound wherein said condensation product comprisingboth a bis phenol derivative and a phosgene derivative is a polymer. Thepresent invention also provides for a stabilized polymer comprisingpolycarbonate resistant to the effects of ultraviolet radiationcomprising said high molecular weight compound.

Additionally the present invention provides for a variety of methods tomanufacture the high molecular weight stabilizing compound of thepresent invention:

1) a first process for the preparation of said high molecular weightstabilizer compound comprising the interfacial condensation of aphosgene derivative and a bis-phenol derivative to produce acondensation product wherein (a) while the phosgene derivative and thebisphenol derivative are reacted in the presence of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid and a suitable catalyst, (b) a base is subsequently added;

2) a second process for the preparation of said high molecular weightstabilizing compound comprising the melt trans-esterification of acarbonate ester and a bis-phenol derivative wherein (a) a carbonateester and a bisphenol derivative are mixed together along with3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid and a suitable catalyst and, (b) heating the blend under conditionsof reduced pressure whereby condensation polymerization occurs;

3) a third process for the preparation of said high molecular weightstabilizing compound comprising (a) melting a polymer comprisingpolycarbonate, and (b) adding thereto3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid; and

4) a fourth process for the preparation of said high molecular weightstabilizer compound comprising (a) mixing a polymer comprisingpolycarbonate and3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid, (b) feeding the mixture to an extruder, and (c) processing themixture under conditions of melt processing at a temperature sufficientto effect reaction. It is to be understood that when the compound3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid is referred to herein, structural variants as hereinafter describedand as described in U.S. Pat. Nos. 4,853,471; 4,973,702; and 5,032,498may be substituted to achieve the same purpose.

The present invention further provides for articles of manufacturecomprising the high molecular weight stabilizer compound of the presentinvention. Such articles of manufacture may exist in a variety of formssuch as sheet, film, molded articles, and the like. Particularly usefulapplications for the compound of the present invention would include,but are not limited to, articles such as glazing materials, automobileheadlight and taillight lenses, eyeglass lenses, and other uses wherethe both the physical optical properties of the materials comprising thecompound of the present invention would render such use advantageous.Other particularly useful applications for the compounds of the presentinvention include articles such as sheet manufactured by coextrusion ormolded articles manufactured by an insert injection molding processwhereby the high molecular weight stabilizing compound of the presentinvention is present as a protective layer or as a protective surfacelayer, with the remainder of the article being a resin or mixture ofresins, preferably polycarbonate or copolymers thereof that wouldbenefit from such layering or protective layering.

Thus, the present invention overcomes the problems associated withdecreases in stabilizer concentration due to the poor miscibility, poordispersibility or high volatility of the low molecular weight stabilizermolecules, by comparison to the high molecular weight polymer molecule,by converting a monomeric stabilizer molecule into a functionalizedpolymeric molecule, simultaneously preserving the stabilizing function,lowering the volatility, and improving the miscibility or dispersibilityof the stabilizing polymer molecule. This reduces losses of expensivestabilizer compounds during processing of polymers, and reduces downtimeduring manufacturing. The polymers so created may be used as stabilizersin polymers, polymer alloys or formulated into products directly.

DETAILED DESCRIPTION OF THE INVENTION

There is provided by the present invention, a chain stopper selectedfrom the group of compounds having the formula: ##STR3## where R₁ isselected from the group of two to twelve carbon atom alkyl groups,preferably branched alkyl groups containing four to twelve carbon atoms,and R₂ is selected from the group of hydrogen or one to twelve carbonatom alkyl groups and where n ranges from zero to about twelve, usefulfor terminating or chain stopping polycarbonate comprising polymers.

There is provided by the present invention, a polycarbonate compositioncomprising a chain stopper selected from the group of compounds havingthe formula: ##STR4## where R₁ is selected from the group of two totwelve carbon atom alkyl groups, preferably branched alkyl groupscontaining four to twelve carbon atoms, and R₂ is selected from thegroup of hydrogen or one to twelve carbon atom alkyl groups and where nranges from zero to about twelve, and a bisphenol of the formula:##STR5## where each R⁵ is independently selected from the groupconsisting of hydrogen, alkyl groups of from one to about nine carbonatoms, and aryl groups of from six to about fifteen carbon atoms,wherein the polycarbonate is useful for the various applications knownfor polycarbonate comprising polymers, and wherein the polycarbonate isuseful as a stabilizer against the degradative effects of ultravioletradiation for other polycarbonate comprising formulations.

There is provided by the present invention a method for making to thepolycarbonate composition of the present invention, comprising,

(a) effecting reaction under interfacial reaction conditions at a pH inthe range of about 7 to about 12 with a chain-stopper selected from thegroup of compounds having the formula: ##STR6## where R₁ is selectedfrom the group of two to twelve carbon atom alkyl groups, preferablybranched alkyl groups containing four to twelve carbon atoms, and R₂ isselected from the group of hydrogen or one to twelve carbon atom alkylgroups and where n ranges from zero to about twelve, and a bisphenol ofthe formula: ##STR7## where each R⁵ is independently selected from thegroup consisting of hydrogen, alkyl groups of from one to about ninecarbon atoms, and aryl groups of from six to about fifteen carbon atoms,and a substantially stoichiometric amount of phosgene in the presence ofan amount of a tertiary amine catalyst having the formula:

    R.sup.6.sub.3 N

and optionally a phase transfer catalyst, where each of the R⁶ areindependently selected from the group of C₂ to C₁₀ alkyl radicals andwhich is effective for providing polycarbonate. The lowest molecularweight oligomeric molecule exemplary of the compounds of the presentinvention is a carbonate of bis-phenol A comprising one carbonate unitand two units of bis phenol A and two chain stopping molecules,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid condensed to form an ester linkage between the terminal phenolhydroxy group of the two bis phenol moieties and the carboxylic acidfunctionality of the chain stopper having a molecular weight of at least1,125. The di-ester of bis phenol A with3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-propanoicacid is also a stabilizing molecule of the present invention, having amolecular weight of 871.

Some of the bisphenols which are included within the herein abovedisclosed formula for bisphenol are, for example:

2,2-bis(4-hydroxy phenyl)propane (bisphenol A)

2,2-bis(4-hydroxy phenyl)butane (bisphenol B)

4,4-bis(4-hydroxy phenyl)heptane

2,2-bis(4-hydroxy phenyl)hexane

2,2-bis(4-hydroxy phenyl)pentane

2,2-bis(4hydroxy phenyl)-4-methyl pentane

2,2-bis(4-hydroxy phenyl)heptane, and

3,3-bis(4-hydroxy phenyl)2,4-dimethyl pentane.

Some of the phase transfer catalysts which are included within formula(1) are for example:

CH₃ (CH₂)₃ !₄ NX

CH₃ (CH₂)₅ !₄ NX

CH₃ (CH₂)₆ !₄ NX, and

CH₃ CH₃ (CH₂)₃ !₃ NX

where X is selected from Cl--, Br-- or --OR⁴ where R⁴ is selected fromthe group consisting of alkyl radicals having from one to nine carbonatoms.

In addition to the phase transfer catalysts of the previously disclosedformula, there are also included phase transfer catalysts having theformulas,

CH₃ (C₄ H₉)₃ NX,

CH₃ (C₄ H₉)₃ PX,

C₂ H₅ (C₆ H₁₃)₃ NX,

(C₄ H₉)₃ N--(CH₂)₆ --N(C₄ H₉)₃ 2X,

(C₃ H₇)₃ N--(CH₂)₆ --N(C₃ H₇)₃ 2X, and

CH₃ (C₅ H₁₁)₂ N--(CH₂)₄ --N(C₅ H₁₁)₂ CH₃ 2X

where X is as previously defined.

In the practice of one form of the present invention, a mixture ofbisphenol and a chain-stopper of the invention is phosgenated underinterfacial reaction conditions in the presence of an organic solvent,in the presence of an effective amount of a polymerizing catalyst. Whilenot wishing to be bound by any particular theory, it is believed thatthe chain stopper reacts with the growing live end of the polymer toform an ester linkage through the acid substituent of the phenolicsubstituent of the substituted benzotriazole. Since this mode ofreaction leaves the phenolic hydroxyl group free to dissociate orhydrogen bond the stabilizing properties of the stabilizing chainstopper molecule remain undisturbed by this particular chemicalreaction. Generally the quantity of catalyst used ranges from about 0.05mole % to about 10.00 mole % catalyst based on the total moles ofbisphenol and chain stopper present in the reaction medium; suchquantity constituting an effective amount. The quantity of tertiaryamine when used as a catalyst ranges from about 0.01 to 6.00 mole %based on the moles of bis-phenol-A present in the reaction medium, amore preferred range is 0.01 to 4.00 mole %, and the most preferredrange is 0.20 to 2.50 mole %. Suitable organic solvents which can beused are, for example, chlorinated aliphatic hydrocarbons, such asmethylene chloride, chloroform, carbon tetrachloride, dichloroethane,trichloroethane, tetrachloroethane, dichloropropane and1,2-dichloroethylene; substituted aromatic hydrocarbons such as,chlorobenzene, o-dichlorobenzene, and the various chlorotoluenes. Thechlorinated aliphatic hydrocarbons, especially methylene chloride, arepreferred.

Sufficient alkali metal hydroxide can be utilized to raise the pH of thebisphenol reaction mixture to 10.5 prior to phosgenation to providedissolution of some of the bisphenol and chain-stopper into the aqueousphase.

Aqueous alkali, or alkaline earth metal hydroxide can be used tomaintain the pH of the phosgenation mixture which can be in the range ofbetween about 7 to about 12 and preferably 8 to 11. Various methods ofcontrolling pH exist during the reaction, a specifically preferredtechnique is taught in U.S. Pat. No. 5,025,081 herein incorporated byreference. Some of the alkali metal or alkaline earth metal hydroxides,which can be employed are for example, sodium hydroxide, potassiumhydroxide, and calcium hydroxide. Sodium and potassium hydroxides andparticularly sodium hydroxide is preferred.

Phosgenation of the bisphenol can be conducted in a wide variety ofeither batch or continuous reactors. Such reactors are, for example,stirred tank reactors, which may be either batch or continuous flow.Additional reactors which are included are agitated column andrecirculating loop continuous reactors.

The volume ratio of aqueous to organic phase during and at thetermination of the phosgenation reaction can be in the range of 0.2-1.1.Reaction temperature can be in the range of between about 15-50° C. Whenthe preferred organic liquid is utilized, such as methylene chloride,the reaction may be conducted at reflux which can be 35°-42° C. Thereaction can be conducted at atmospheric pressures, although sub- orsuperatmospheric pressures may be employed if desired.

During phosgenation, the mixture is agitated, such as, by using astirrer or other conventional equipment. The phosgenation rate can varyfrom between about 0.02-0.2 mole of phosgene, per mole of bisphenol perminute.

Prior to polycarbonate recovery which can be achieved by standardtechniques, such as filtration, decantation, and centrifugation,chloroformate end groups are normally substantially eliminated. Thereaction mixture sometimes must be agitated for a long period of timeuntil the presence of chloroformates can no longer be detected.Alternatively, the addition of an equivalent level of a phenoliccompound, based on the level of chioroformate, can be added at the endof the reaction.

Depending upon the molecular weight of polycarbonate desired,chain-stoppers can be used in a proportion of from 0.05 to 8 mole %based on the total moles of bisphenol and chain-stopper. The compositionof the present invention utilizes as a chain stopper the compound,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid, or homologs thereof as previously defined by the general formulaherein before recited, non limiting examples are:3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-ethanoicacid,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-methanoicacid,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenebutanoicacid,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-pentanoicacid,3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzene-isobutanoicacid, and the like. The quantity of chain stopper present in thesynthesized polymer ranges from about 0.07 up to about 14 weightpercent, more preferably from about 1 to about 12 weight percent andmost preferably from about 2 to about 10 weight percent based on thecomposition of the finished polymer. The percentage of chain stopperpresent in polymer alloys comprising the high molecular weightstabilizer will vary according to the amount of chain stopper present inthe high molecular weight polymeric stabilizer as synthesized and thequantity of other polymers alloyed therewith.

The forgoing describes the preparation of polycarbonate comprisingpolymers wherein the stabilizing molecule functioning as a chainstopperis directly incorporated into the termini of the polymer molecule as thepolymer is being synthesized. Mixtures of chain stoppers may be employedto vary the mole ratio of stabilizing chain stopping molecules to thosewhich have other functions or which merely function as chain stoppingagents solely. Alternative methods of incorporating chain stoppingagents may be employed such as trans-esterification. Under conditions oftrans-esterification, the polymer is prepared at a higher averagemolecular weight than would be utilized in the final product. Thepolymer is then admixed with a suitable quantity of one or more chainstopping stabilizer compound(s) or mixture thereof followed by theoptional addition of one or more trans-esterification catalysts andtrans-esterified. The quantity of stabilizing chain stopping compound iscalculated based on the desired final average molecular weight of thepolymer. This process serves to incorporate the stabilizing chainstopping compound while reducing the molecular weight of the polymer.This process may be accomplished in a reaction vessel, with or withoutthe catalyst, or as is demonstrated in the experimental section, it mayaccomplished under conditions of melt extrusion in an extruder.

One particular approach to transesterification is the reaction ofcarboxylic acid functional groups with polycarbonate resin. In U.S. Pat.Nos. 5,081,205; 4,960,839; 4,826,928; and 4,999,408; a carboxylic acidfunctional group attached as a side group or as a pendant group reactsvia transesterification forming a cross link with another polymer chain.In U.S. Pat. No. 4,814,395, a carboxylic acid functional group attachedas an end group on a polycarbonate chain reacts by thistransesterification to yield a polycarbonate chain with hydroxyl endgroups. In U.S. Pat. No. 4,762,896, an additive compound that iscarboxylic acid functional such as stearic acid will react with apolycarbonate polymer to reduce the molecular weight of the polymer. Inthese examples, it is hypothesized that a carboxylic acid group reactswith a carbonate group in the polycarbonate resin, thereby generatingtwo new polymer end groups and simultaneously reducing polymer molecularweight by cutting the polymer chain into two smaller polymer molecules.The reaction as hypothesized, proceeds according to the following path:

    ArOCO.sub.2 Ar+RCO.sub.2 H→CO.sub.2 +ArOH+RCO.sub.2 Ar

generating a new ester linkage, a phenolic hydroxy end group, with theevolution of carbon dioxide. In the above reaction sequence, R is analkyl or aryl group and Ar stands for a segment of a polycarbonatepolymer.

An alternative approach to transesterification is the reaction of acarboxylate or carbonate ester functional group with a polycarbonateresin, utilizing an appropriate catalyst. The reaction is hypothesizedto proceed along the following path: ##STR8## where Ar and R are asdefined before and R' is a different alkyl or aryl group.

Transesterification of polycarbonate polymers leads to at least threeoutcomes regarding measurable characteristics of the polymers, whichoutcomes are useful in measuring the extent to which thetransesterification reaction has proceeded. First, when additional endgroups are incorporated into the polymer the average molecular weighthas been reduced. Second, incorporation of the carboxylic acid or esterinto the polymer can be detected by analysis of the reacted polymer.Third, the amount of the unreacted or residual material may be analyzed.When the stabilizing end capping or chain stopping molecule has beenincorporated into the polymer it may be detected by chemical or physicalmeans; such incorporation at very low levels may be only slightlygreater than zero. By the phrase, greater than zero, Applicant definesgreater than zero as present in the polymer in a chemically orphysically measurable amount using techniques known in the art.

Trans-esterification of polyester or polycarbonate type polymers, i.e.polycarbonate comprising polymers or copolymers and/or polyester orcopolyester polymers, such as disclosed in the teachings of the instantinvention, may lead to two outcomes. Two polymers may be melted togetherin the presence of a suitable catalyst and if there are presentdifferent chain stopping groups terminating the two polymers,transesterification and ester group exchange may be detected in theproduct. Alternatively, a given polymer may be melted in the presence ofadditional quantities of chain stopping agent either with or without atrans-esterification catalyst and the chain stopper will be incorporatedinto the polymer with a consequent reduction in molecular weight

Polymer precursors to the stabilized and stabilizing polymers of thepresent invention may be made by a variety of techniques. Polycarbonatesmay be made by the techniques disclosed and taught in U.S. Pat. No.3,030,331; 3,169,121; and 3,275,601 herewith incorporated by reference.Polyester polycarbonate copolymers may be made by the techniquesdisclosed and taught in U.S. Pat. Nos. 3,303,331; 4,194,038; 4,159,069;4,188,314; and 4,923,933 herewith incorporated by reference.Polycarbonate siloxane copolymers may be made by the techniquesdisclosed in U.S. Pat. Nos. 3,419,634; 3,832,419; and 4,681,922. Thepolymer precursors are endcapped with an end stopping compound selectedfrom the group of compounds having the formula: ##STR9## leading to thepolymers of the present invention.

There is further provided by the present invention articles ofmanufacture comprising the stabilizing polymer of the present invention.A non-limiting example of such an article of manufacture would be anextruded sheet or film manufactured either wholly or in part from thestabilized polymer of the present invention.

All of the U.S. patents referenced herein are herewith specificallyincorporated by reference.

EXPERIMENTAL

The following laboratory preparations indicate a reduction to practiceof specific examples and embodiments of the present invention. On alaboratory scale, these examples are a demonstration of the best modeknown to the inventor at the time of filing this application. Commercialscale embodiments of the various embodiments of this invention arebelieved to be achievable by the application of known techniques in theart of chemical reaction engineering and thus are intended to be coveredby the claims appended hereto absent novel, unobvious, and unexpecteddifficulties or problems associated with scale-up from laboratory scalepreparations to commercial scale preparations.

Analysis of resin samples for covalently bound3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid residues was carried out by dissolving one gram of resin in 10 mlof methylene chloride, adding the methylene chloride solution of resindropwise with stirring to 50 ml of acetone, then collecting and dryingthe precipitate. The level of covalently bound3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid present was determined by UV adsorption at 343 nm wavelength usingthe assumption that the molar extinction coefficient of covalently bound3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid was essentially identical to that for free3-(2H-benzotriazol-2-yl)-5-(1,1-diethylethyl)-4-hydroxy-benzenepropanoicacid.

Analysis of resin samples for3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid was conducted by extraction of one gram of resin with 10 ml ofacetonitrile, followed by a liquid chromatographic analysis with 70/30acetonitrile/water to 100% acetonitrile over 15 minutes, then a 15minute hold at 100% acetonitrile using a C-18 Bondapack column. Analysisof resin samples for molecular weight was conducted by gel permeationchromatographic analysis using a Waters Associates Model 150C instrumentfitted with two ultrastyragel linear columns and one 500 angstromultrastyragel column, using chloroform as the solvent. The instrumentwas calibrated using bisphenol-A polycarbonate resin standards.

EXAMPLE 1

Hydrolysis of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid, 1,6-hexandiyl ester (available commercially as Tinuvin 840®(fromCiba-Geigy): In a 1000 ml round bottom flask fitted with a heatingmantel, magnetic stirrer, and a condenser capped with a drying tube weremixed 650 ml methanol and 56.0 g (1.0 mole) potassium hydroxide (KOH).After dissolution of the KOH, 190 g (0.25 mole) of3-(2H-berzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid, 1,6-hexandiyl ester was added. Upon heating to reflux, thereaction mixture turned to a clear dark red solution. Refluxing wascontinued for two days, with no visual change in the reaction mixture.The solids remained in solution upon cooling to room temperature.Acidification of the mixture with excess aqueous hydrochloric acidyielded a copious precipitate which was collected in a Buechner funnel,washed with a large excess of methanol and air dried. The material had amelting point of 190-195° C. Infrared analysis showed a typicalcarboxylic acid absorption peak at 1700 cm⁻⁴. The melting point forTinuvin 8400®(is 115-119° C. After recrystallization from ethyl acetate,the material had a melting point of 191-195° C. The compound prepared is3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxybenzenepropanoicacid. Liquid chromatographic analysis indicated that the product as madecontained approximately 11% methyl ester.

EXAMPLE 2

Preparation of Polycarbonate endcapped with of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxybenzenepropanoicacid: A 2000 ml four neck flask was fitted with a mechanical stirrer, apH probe, a gas inlet tube, and a Claisen adapter fitted with a dry icecondenser and an aqueous caustic inlet tube. To the flask was added 325ml of water, 400 ml of methylene chloride, 57 g (0.25 mole) bisphenol-A,0.7 ml (0.005 mole, 2 mole %) triethyl amine, and 2.63 g (0.0077 mole,3.1 mole %) of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxybenzenepropanoicacid, as prepared in example 1. Phosgene was introduced into the flaskat a rate of 1 g/min. for thirty minutes holding the pH of the aqueousphase at a pH of 8 for the first 12 minutes of reaction and then holdingthe pH of the aqueous phase at a pH of 10.2 thereafter. At the end ofthe reaction the layers quickly separated. The resin solution had aslight yellow color. The methylene chloride layer was washed twice witha 2% aqueous solution of hydrochloric acid and three times with water,followed by drying over magnesium sulfate and precipitated with hotwater in Waring blender. The powder resulting from the precipitate had aslight yellow color. Two additional batches were run in the same manner,with 3.48 g (4.1 mole %) and 3.9 g (4.6 mole %) of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid. Acidification of the brine layer from each of the reactions didnot result in the formation of a precipitate. Results of analyses on thepolycarbonates endcapped with3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid are presented in Table 1.

                  TABLE 1    ______________________________________    Polycarbonate Endcapped with 3-(2H-benzotriazol-2-yl)-5-(1,1-    dimethylethyl)-4-hydroxy-benzenepropanoic acid.            Mole %    Preparation            Endcapper                     Weight % MW    MN    Disp T.sub.g ° C.    ______________________________________    A       3.1      4.2      35,100                                    11,500                                          3.07 151    B       4.1      5.6      28,200                                    9,800 2.88 149    C       4.6      6.2      24,300                                    8,400 2.88 147    ______________________________________

The molecular weights of the three samples prepared are essentiallyidentical to the molecular weights of the standard, commercial resinsprepared with 3.1, 4.1, and 4.6 mole % conventional monofunctionalend-capping agents (after making allowance for the fact that thecarboxylic acid functional end-capping agent used herein containedapproximately 11% of unreacted methyl ester). A liquid chromatographicanalysis (LC) of the three resin samples in Table 1 indicated that lessthan 0.03 mole % of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid initially mixed with the polymer was present in an unreacted form.This strongly suggests complete incorporation of3-(2-H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid in the resin. An analysis of sample A (Table 1) for covalentlybound3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid showed 4.6 weight percent present in the re precipitated resin,confirming essentially complete incorporation. The variations betweenexpected and theoretical are attributed to analytical precision and thepossibility of some selective precipitation of the polymer bearing the3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid functionality.

Based on the known reactivity of carboxylic acids under these reactionconditions (i.e. mono carboxylic acids incorporated as end caps as inU.S. Pat. No. 4,431,793 or dicarboxylic acids incorporated asco-monomers as in U.S. Pat. No. 5,025,081) and the molecular weight dataindicating that3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid incorporated as a monofunctional reagent, i.e. as an end-capping;the results obtained show that the highly hindered phenolic group in3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroy-benzenepropanoicacid did not react under the reaction conditions employed. Thisconclusion is based on the assumption that if the phenolic hydroxy groupof3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid had been reactive, the compound would have been incorporated as aco-monomer resulting in a resin having a very high molecular weight dueto the absence of an effective end-capping reagent.

EXAMPLE 3

Preparation of the bisphenol-A di-ester of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid(2,2-bis(4-hydroxophenyl)propyl-bis-(3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoate):In a round bottom flask fitted with a condenser capped with a dryingtube were mixed 33.9 g (0.1 mole) of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid, 30 ml of dry toluene, and 12 ml (0.156 mole) thionyl chloride.After 30 minutes of stirring at room temperature with no evidence ofreaction, the flask was warmed to slightly below the reflux temperaturewhich resulted in the evolution of gaseous hydrogen chloride. After fourhours of reaction time, a sample was taken and subjected to analysis byinfrared spectrophotometry, which indicated by virtue of a stronginfrared absorption peak at 1796 cm⁻¹ that reaction was complete. Afterfive and one half hours, the heat being supplied to the reaction wasdiscontinued and the reaction mixture was allowed to stand three days.75 ml of dry toluene was added to the reaction mixture and 50 ml oftoluene was distilled away from the reaction mixture by a vacuumdistillation, where the vacuum was created by aspiration, to removeexcess thionyl chloride. The flask was cooled. To the contents of thecooled flask, 11.4 g bisphenol-A (0.05 mole) and 17.5 ml triethyl aminedissolved in 50 ml dry toluene were added. After reacting for two hours,crystals formed which were collected on a Buechner funnel. Removal ofthe solvent from the mother liquor yielded an oil which eventuallycrystallized. The two crystalline samples were washed with methanol anddetermined to be identical by comparison of their respective infraredabsorption spectra. The combined weight of crystals recovered was 33.9g. The crystalline material was recrystallized from toluene to yield 21g of a slightly yellow crystalline solid which had a proton nmr spectrumin agreement with the structure of2,2-bis(-4-hydroxophenyl)propyl-bis-(3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoate). Liquidchromatographic analysis indicated that the product as made containedapproximately 4% unknown material.

EXAMPLE 4

Melt Trans-esterification of Polycarbonate Resin to Incorporate aStabilizing Chain Stopper. Melt trans-esterification may be accomplishedby any of several techniques known in the art. A particularly usefulmeans of trans-esterifying the polymers of the present invention is toutilize a heated extruder as the reaction vessel in a so-called reactiveextrusion. A quantity of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid sufficient to produce a 2 mole % level was blended into 450 g of apolycarbonate having a molecular weight of 33,000. Using a 3/4" Wayneextruder, the mixture of polycarbonate and3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid was extruded at 600° F. Incorporation of 2 mole % should generateapproximately 4 mole % new end groups with the result that molecularweight of the polymer would be reduced, Table 2.

                  TABLE 2    ______________________________________    Reactive Extrusion of Polycarbonate with Stabilizing End    Capping Agent (3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-    4-hydroxy-benzenepropanoic acid).                       Mole %             Mole %    Stabilizing                                  Mol. Wt.                                         Mol. Wt.    Resin    End Capping                       End Capper (MW)   (MN)    ______________________________________    Reference             2.4       0          33,000 17,400    Resin #1    Example 4A             2.4       2.0        18,500 7,600    Example 4B             2.4       2.0        17,400 7,000    Resin #2 6.5       0          16,700 7,700    ______________________________________     Notes:     4A Sample taken at the beginning of the extrusion.     4B Sample taken at the end of the extrusion.

Melt transesterification, conducted as a reactive extrusion, reduced themolecular weight of the reference resin #1 from about 33,000 to about18,000. For comparative purposes, molecular weight data on a standard,commercial reference resin, resin #2, prepared by the conventional meansusing 6.5 mole % end-capping agent (4.1 mole % more end-capping resinthan reference resin #1) is given in Table 2. Inspection of the datashows that the two transesterified resin samples, 4A and 4B, are veryclose in molecular weight to the reference resin #2. This indicates thatthose two resins possess approximately 6.5% mole end groups.Consequently, transesterification generated an additional 4 mole % endgroups in the reference resin #1, as would be predicted based on competereaction of the 2 mole % acid supplied in the transesterification.

EXAMPLE 5

Melt Transesterification of Polycarbonate Resin to Incorporate aStabilizing Chain Stopper (larger scale example at a lower processingtemperature) A quantity of3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid sufficient to produce a 3.6 mole % level (4.6 weight %) was blendedinto 1800 g of a polycarbonate resin having a molecular weight of33,000. The3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid was prepared as in Example 1 with the addition of a finalrecrystallization using ethyl acetate. Minor amounts of epoxy andphosphite stabilizers as well as an optical brightener were blended in.The blend was extruded into pellets on a Werner-Pfleiderer SK30 twinscrew extruder with temperature zones set at 465° F. to 480° F. Thepellet sample was directly analyzed for polymer bound3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid by re precipitation and UV analysis. Residual unreacted3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid was analyzed for by LC. The results are set forth in Table 3.

                  TABLE 3    ______________________________________    Reactive Extrusion of Polycarbonate with Stabilizer End    Capping Agent 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-    hydroxy-benzenepropanoic acid (BzTrzl) (lower temperature extrusion    with a second melt processing step)                          Analysis for BzTrzl    Formulated Levels               Melt       Molecular Wt. % Wt. %    Mole %          Wt. %    Processing Weight  Bound Free    ______________________________________    3.6   4.6      single ext.                              15,800  1.4   2.8                   465-480° F.    3.6   4.6      single plus                              10,700  --    0.5                   add'l. 1.5 min.                   at 500° F.    3.6   4.6      single plus                               9,900  --    0.38                   add'l. 2 min.                   at 500° F.    3.6   4.6      single plus                               9,500  --    0.13                   add'l 3 min,                   at 500° F.    ______________________________________     Notes: All samples received are 465-480° F. twin screw extrusion     with additional 500° F. second processing steps as indicated. The     reported molecular weights are weight average molecular weight.

The results shown in table 3 indicate that a single reactive extrusionat 465-480° F. does not result in complete reaction of the3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid. Of the initial 4.6 wt. % in the formulation, 1.4 wt. % isaccounted for as a bound end-capping agent and the remaining 2.8 wt.%found as unreacted residue. The variance between 4.2 and 4.6 wt. % isattributed to uncertainties in analytical precision and accuracy sinceother reaction products of the3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid were not analyzed for. This is conceivably the case in short chainoligomers containing bound3-(2H-benzotriazol-2-yl)-5-(1,1-dimthylethyl-4-hydroxy-benzenepropanoicacid that failed to re-precipitate. Repetition of the foregoingexperiment with3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid that had not been recrystallized from ethylacetate resulted in asample having 1.7 wt. % free3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid after the first extrusion. Repetition of this experiment withhigher viscosity polycarbonate (higher molecular weight) resinessentially duplicated the results.

EXAMPLE 6

Melt Trans-esterification of Polycarbonate Resin to Incorporate aStabilizing Chain Stopper (repeat melt processing, with optionaladditional catalysts). Samples of pellets prepared in Example 5 weredried at 115° C. for 2 hours, then starve fed into a small-scale benchtop extruder (CSI MAX mixing extruder manufactured by Custom ScientificCorp.) set at 500° F. (260° C.) and 60 rpm. The minimum residence timefor resin being processed by the extruder was approximately one minute.Longer residence times were obtainable by temporarily plugging theoutlet of the extruder. Catalytic materials, e.g. acids and bases, wereadded to the pellet samples by dispersing quantities of the catalyticmaterial onto samples of the polycarbonate resin producing a resincatalyst concentrate such that when 1 wt. % of the resin catalystconcentrate was added to the pellets from Example 5 the levels ofcatalyst listed in Table 4 were obtained.

The results of Table 3 demonstrate clearly that incremental additions ofmelt reaction processing in an extruder increase the approach tocompletion of the reaction between the polycarbonate polymer and the3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoicacid end capping reagent. The results in Table 4 show that a basiccatalyst accelerated melt transesterification and that a mildly acidiccatalyst was not particularly effective at promoting a faster melttransesterification. This result might be explainable on the basis thatextremely low levels of base (parts per billion or low parts permillion) are carried over into the resin product and act to catalyzetransesterification. More aggressively acidic and basic materials areknown to catalyze transesterification.

                  TABLE 4    ______________________________________    Reactive Extrusion of Polycarbonate with Stabilizing End    Capping Agent, 3-(2H-benzotriazol-2-yl)-5-(1,1-dimethylethyl)-4-    hydroxy-benzenepropanoic acid (second melt processing step with    added catalyst)    Duration of                      Weight    Second Melt             Molecular                                     Percent Free    Processing (min.)                Catalyst    Weight   BzTrzl    ______________________________________    0           none        15,800   2.8    1.5         none        10,700   0.5    2.0         none        9,900    0.38    3.0         none        9,500    0.13    1.5         200 ppm     13,900   --                acid    2.0         200 ppm     13,800   --                acid    3.0         200 ppm     14,800   --                acid    1.0         none        9,900    0.081    1.5         none        9,300    0.0066    2.0         none        8,850    NDA    1.0         0.025 mole %                            9,800    0.049                base    1.5         0.025 mole %                            9,000    0.0051                base    2.0         0.025 mole %                            9,200    0.0055                base    ______________________________________     Notes to Table 4:     1. All samples were prepared such that the level of     3(2H-benzotrizol-2-yl)-5-(1,1-dimethylethyl)-4-hydroxy-benzenepropanoic     acid was 3.6 mole % (4.6 weight %).     2. All samples received a first melt processing step at 465-480° F     as well as the second melt processing described in the Table.     3. The acid catalyst used was 2:1 weight ratio blend of     tris(nonylphenyl)phosphite to phosphorus acid.     4. The base catalyst used was tetraethylammonium hydroxide.     5. The two sets of samples reprocessed without catalyst were run in     separate experiments and serve as controls respectively, for the acid and     base experiments listed below them in the Table. For both, essentially     complete reaction was observed after 2-3 minutes of reprocessing. The     differences between them are attributable to the variation in reaction     temperature and reaction time that typically occur when using small scale     extrusion apparatus.

Having described the invention that which is claimed is:
 1. A di-estercompound of the formula: ##STR10## where each R⁵ is independentlyselected from the group consisting of hydrogen, alkyl groups of from oneto about nine carbon atoms, and aryl groups of from six to about fifteencarbon atoms, and E is an esterified acid selected from the group ofacids having the formula: ##STR11## where R₁ is selected from the groupof two to twelve carbon atom alkyl groups, R₂ is selected from the groupof hydrogen or one to twelve carbon atom alkyl groups and n varies from0 to 20; wherein the ester linkages of said di-ester is formed from thecarboxylate group of said acid and wherein the molecular weight is atleast 871.